CVE-2013-0228 xen: xen_iret() invalid %ds local DoS (rhbz 910848 906309)
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Josh Boyer
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11
kernel.spec
11
kernel.spec
@ -62,7 +62,7 @@ Summary: The Linux kernel
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# For non-released -rc kernels, this will be appended after the rcX and
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# gitX tags, so a 3 here would become part of release "0.rcX.gitX.3"
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#
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%global baserelease 1
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%global baserelease 2
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%global fedora_build %{baserelease}
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# base_sublevel is the kernel version we're starting with and patching
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@ -745,6 +745,9 @@ Patch21247: ath9k_rx_dma_stop_check.patch
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#rhbz 910126
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Patch21249: pstore-Create-a-convenient-mount-point-for-pstore.patch
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#rhbz 906309 910848 CVE-2013-0228
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Patch21260: xen-dont-assume-ds-is-usable-in-xen_iret-for-32-bit-PVOPS.patch
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Patch22000: weird-root-dentry-name-debug.patch
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#selinux ptrace child permissions
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@ -1455,6 +1458,9 @@ ApplyPatch ath9k_rx_dma_stop_check.patch
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#rhbz 910126
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ApplyPatch pstore-Create-a-convenient-mount-point-for-pstore.patch
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#rhbz 906309 910848 CVE-2013-0228
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ApplyPatch xen-dont-assume-ds-is-usable-in-xen_iret-for-32-bit-PVOPS.patch
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# END OF PATCH APPLICATIONS
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%endif
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@ -2310,6 +2316,9 @@ fi
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# ||----w |
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# || ||
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%changelog
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* Thu Feb 14 2013 Josh Boyer <jwboyer@redhat.com>
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- CVE-2013-0228 xen: xen_iret() invalid %ds local DoS (rhbz 910848 906309)
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* Wed Feb 13 2013 Peter Robinson <pbrobinson@fedoraproject.org>
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- Disable tegra30
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131
xen-dont-assume-ds-is-usable-in-xen_iret-for-32-bit-PVOPS.patch
Normal file
131
xen-dont-assume-ds-is-usable-in-xen_iret-for-32-bit-PVOPS.patch
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@ -0,0 +1,131 @@
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From 13d2b4d11d69a92574a55bfd985cfb0ca77aebdc Mon Sep 17 00:00:00 2001
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From: Jan Beulich <JBeulich@suse.com>
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Date: Thu, 24 Jan 2013 13:11:10 +0000
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Subject: [PATCH] x86/xen: don't assume %ds is usable in xen_iret for 32-bit
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PVOPS.
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This fixes CVE-2013-0228 / XSA-42
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Drew Jones while working on CVE-2013-0190 found that that unprivileged guest user
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in 32bit PV guest can use to crash the > guest with the panic like this:
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-------------
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general protection fault: 0000 [#1] SMP
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last sysfs file: /sys/devices/vbd-51712/block/xvda/dev
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Modules linked in: sunrpc ipt_REJECT nf_conntrack_ipv4 nf_defrag_ipv4
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iptable_filter ip_tables ip6t_REJECT nf_conntrack_ipv6 nf_defrag_ipv6
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xt_state nf_conntrack ip6table_filter ip6_tables ipv6 xen_netfront ext4
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mbcache jbd2 xen_blkfront dm_mirror dm_region_hash dm_log dm_mod [last
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unloaded: scsi_wait_scan]
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Pid: 1250, comm: r Not tainted 2.6.32-356.el6.i686 #1
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EIP: 0061:[<c0407462>] EFLAGS: 00010086 CPU: 0
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EIP is at xen_iret+0x12/0x2b
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EAX: eb8d0000 EBX: 00000001 ECX: 08049860 EDX: 00000010
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ESI: 00000000 EDI: 003d0f00 EBP: b77f8388 ESP: eb8d1fe0
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DS: 0000 ES: 007b FS: 0000 GS: 00e0 SS: 0069
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Process r (pid: 1250, ti=eb8d0000 task=c2953550 task.ti=eb8d0000)
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Stack:
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00000000 0027f416 00000073 00000206 b77f8364 0000007b 00000000 00000000
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Call Trace:
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Code: c3 8b 44 24 18 81 4c 24 38 00 02 00 00 8d 64 24 30 e9 03 00 00 00
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8d 76 00 f7 44 24 08 00 00 02 80 75 33 50 b8 00 e0 ff ff 21 e0 <8b> 40
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10 8b 04 85 a0 f6 ab c0 8b 80 0c b0 b3 c0 f6 44 24 0d 02
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EIP: [<c0407462>] xen_iret+0x12/0x2b SS:ESP 0069:eb8d1fe0
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general protection fault: 0000 [#2]
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---[ end trace ab0d29a492dcd330 ]---
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Kernel panic - not syncing: Fatal exception
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Pid: 1250, comm: r Tainted: G D ---------------
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2.6.32-356.el6.i686 #1
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Call Trace:
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[<c08476df>] ? panic+0x6e/0x122
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[<c084b63c>] ? oops_end+0xbc/0xd0
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[<c084b260>] ? do_general_protection+0x0/0x210
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[<c084a9b7>] ? error_code+0x73/
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-------------
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Petr says: "
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I've analysed the bug and I think that xen_iret() cannot cope with
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mangled DS, in this case zeroed out (null selector/descriptor) by either
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xen_failsafe_callback() or RESTORE_REGS because the corresponding LDT
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entry was invalidated by the reproducer. "
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Jan took a look at the preliminary patch and came up a fix that solves
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this problem:
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"This code gets called after all registers other than those handled by
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IRET got already restored, hence a null selector in %ds or a non-null
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one that got loaded from a code or read-only data descriptor would
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cause a kernel mode fault (with the potential of crashing the kernel
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as a whole, if panic_on_oops is set)."
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The way to fix this is to realize that the we can only relay on the
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registers that IRET restores. The two that are guaranteed are the
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%cs and %ss as they are always fixed GDT selectors. Also they are
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inaccessible from user mode - so they cannot be altered. This is
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the approach taken in this patch.
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Another alternative option suggested by Jan would be to relay on
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the subtle realization that using the %ebp or %esp relative references uses
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the %ss segment. In which case we could switch from using %eax to %ebp and
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would not need the %ss over-rides. That would also require one extra
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instruction to compensate for the one place where the register is used
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as scaled index. However Andrew pointed out that is too subtle and if
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further work was to be done in this code-path it could escape folks attention
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and lead to accidents.
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Reviewed-by: Petr Matousek <pmatouse@redhat.com>
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Reported-by: Petr Matousek <pmatouse@redhat.com>
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Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
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Signed-off-by: Jan Beulich <jbeulich@suse.com>
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Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
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---
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arch/x86/xen/xen-asm_32.S | 14 +++++++-------
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1 files changed, 7 insertions(+), 7 deletions(-)
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diff --git a/arch/x86/xen/xen-asm_32.S b/arch/x86/xen/xen-asm_32.S
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index f9643fc..33ca6e4 100644
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--- a/arch/x86/xen/xen-asm_32.S
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+++ b/arch/x86/xen/xen-asm_32.S
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@@ -89,11 +89,11 @@ ENTRY(xen_iret)
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*/
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#ifdef CONFIG_SMP
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GET_THREAD_INFO(%eax)
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- movl TI_cpu(%eax), %eax
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- movl __per_cpu_offset(,%eax,4), %eax
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- mov xen_vcpu(%eax), %eax
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+ movl %ss:TI_cpu(%eax), %eax
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+ movl %ss:__per_cpu_offset(,%eax,4), %eax
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+ mov %ss:xen_vcpu(%eax), %eax
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#else
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- movl xen_vcpu, %eax
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+ movl %ss:xen_vcpu, %eax
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#endif
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/* check IF state we're restoring */
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@@ -106,11 +106,11 @@ ENTRY(xen_iret)
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* resuming the code, so we don't have to be worried about
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* being preempted to another CPU.
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*/
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- setz XEN_vcpu_info_mask(%eax)
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+ setz %ss:XEN_vcpu_info_mask(%eax)
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xen_iret_start_crit:
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/* check for unmasked and pending */
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- cmpw $0x0001, XEN_vcpu_info_pending(%eax)
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+ cmpw $0x0001, %ss:XEN_vcpu_info_pending(%eax)
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/*
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* If there's something pending, mask events again so we can
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@@ -118,7 +118,7 @@ xen_iret_start_crit:
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* touch XEN_vcpu_info_mask.
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*/
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jne 1f
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- movb $1, XEN_vcpu_info_mask(%eax)
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+ movb $1, %ss:XEN_vcpu_info_mask(%eax)
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1: popl %eax
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--
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1.7.7.6
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